Polymethine compound, a process for its production, and use of the compound

ABSTRACT

The invention provides a near-infrared absorbing material showing a high sensitivity to a YAG laser having an emission wavelength of 900˜1100 nm as well as a high photothermal conversion efficiency, an original plate for direct printing plate making which utilizes the near-infrared absorbing material, and a novel polymethine compound represented by the following general formula (1), of which the above near-infrared absorbing material is comprised.  
                 
 
     (wherein R 1  and R 3  each independently represents an unsubstituted or substituted alkyl group, a cycloalkyl group of 5˜7 carbon atoms or an unsubstituted or substituted aryl group; R 2  and R 4  each independently represents an unsubstituted or substituted alkyl group or an unsubstituted or substituted aryl group; R 5  and R 6  each independently represents a hydrogen atom, an unsubstituted or substituted alkyl group or an unsubstituted or substituted alkoxy group; L represents an unsubstituted or substituted alkylene group of  2˜4  carbon atoms which is necessary for formation of a cyclic structure; X represents a hydrogen atom, a halogen atom or a substituted amino group; Z represents a charge-neutralizing ion)

FIELD OF THE INVENTION

[0001] The present invention relates to a novel polymethine compound, aprocess for producing said compound, and a near-infrared absorbingmaterial containing said compound. The polymethine compound of theinvention absorbs in the near-infrared region of 900˜1100 nm and can beused not only as a near-infrared absorbing material for laserlight-exploiting image recording, e.g. a near-infrared absorbingmaterial for printing platemaking utilizing a laser beam or a laserthermal recording material, but also as a spectral sensitizing dye forelectron photography or silver halide photography, a dye for opticaldisk use and a dye for the near-infrared red absorption filter forplasma display or the like use, among other applications.

PRIOR ART

[0002] With the recent advances in laser technology, image recordingsystems utilizing laser light for high-speed, high-density, high qualityrecording, for example image recording systems involving conversion oflaser light to heat, such as laser thermal recording materials and laserthermographic copying materials, are under investigation. Furthermore,with the rapid development of electronics associated with the spread ofcomputers and innovations in the field of digital image processingtechnology by way of background, the development of the so-calledcomputer-to-plate technology (CTP platemaking technology), namely thetechnology of producing original plates for printing directly fromdigital data, is underway with a great enthusiasm.

[0003] In an image recording system involving conversion of laser lightto heat (laser thermal recording system) a light absorber aligned withthe laser wavelength is used to form a image. However, unless the laseroutput is increased to a fairly high level, the thermal energy requiredfor image formation cannot be obtained and, therefore, the advent of alight absorber with a good photothermal conversion efficiency is beingdemanded.

[0004] With such a laser thermal recording material, a semiconductorlaser having an emission band in the near-infrared region of 750˜850 nmor a YAG laser having an emission band in the near-infrared region of900˜1100 nm is generally employed.

[0005] In the field of original plate for direct printing plate makingplatemaking technology, as classified by the platemaking technique, thelaser light irradiation method, the thermal head writing method, thelocal voltage application method using pin electrodes, and the ink-jetmethod in which an ink-repellent or ink-layer is formed with ink jets,among others, are known. The laser light method, in particular, issuperior to any other methods in resolution and platemaking speed and,in this area, various image-forming systems are being explored.

[0006] Regarding the CTP platemaking technology utilizing laser light,the photosensitive type and the thermosensitive type are available. Asthe photosensitive type plate material, an electron photographic systemutilizing an organic photoconducter (OPC) and a silver salt systemutilizing a salt of silver, among others, are known but these platematerials require large-size and expensive production equipment and theprice of the plate is higher than the price of the presensitized plate(PS plate). Moreover, there also is the problem associated with disposalof the developer solution.

[0007] The thermosensitive type plate material has the disadvantage oflow sensitivity as compared with the photosensitive type plate materialbut since it can be handled in the ordinary room (lit room), asemiconductor laser with an emission wavelength of 750˜850 nm and a YAGlaser with an emission band of 900˜1100 nm are energetically evaluatedas exposure light sources for platemaking.

[0008] The thermosentive type plate material requires a photothermalconversion layer for the conversion of light to heat. This photothermalconversion layer contains a light-to-heat converting agent, such as anear-infrared absorbing material. This light-to-heat converting agentmust absorb the laser light to be used and, for improved sensitivity,the relevant laser light absorbing capacity and photothermal conversionefficiency must be as high as possible.

[0009] The light-to-heat converting agent includes pigment type and dyetype substances. As the pigment type substance, carbon black isgenerally used but compared with dye type substances its absorption isbroad and low in the absorption capacity for a given laser emission sothat it must be used in a large amount. Moreover, a highly sophisticateddispersion technology is required for kneading it with the image-formingcomponent, resin binder and other materials.

[0010] The dye type substance can be selected from among substanceshaving high absorbing capacities for the laser light to be used, goodcompatibility with the image-forming component, resin binder and othercomponents, and good solubility in the solvent to be used.

[0011] Referring to the thermosensitive plate material, materialssuitable for high-speed printing plates are under investigation andparticularly dye type compounds compatible with high-output YAG lasersare in demand. As dye type compounds, organic compounds absorbing in thewavelength range of 900˜1100 nm, such as phthalocyanine compounds,naphthalocyanine compounds, dithiolene metal complex compounds, aminiumcompounds and immonium compounds, are known. However, these compoundshave several drawbacks such as low absorption coefficient, visible bandabsorption and low solvent solubility.

[0012] Partly because of their high absorption coefficients atabsorption maxima, polymethine compounds are utilized in a broad rangeof fields such as photosensitive dyes for silver salt photography,photosensitive dyes for electron photography, dyes for laser recording,dyes for laser oscillation and so forth. However, few compounds areknown to match YAG lasers.

[0013] At the practical level, the industry knows few YAG laser-matchedorganic compounds absorbing in the 900˜1100 nm region of the spectrum.Meanwhile, in the electronic equipment industry, plasma display(hereinafter referred to briefly as PDP) was developed and has by nowbeen implemented as a main stream of large-screen flat display. PDPinvolves release of an electromagnetic radiation on plasma lightemission and, hence, may cause erratic actions in the remote control ofother household electrical appliances owing to the electromagneticradiation (near-infrared rays). For the prevention of such erraticactions of other appliances, it was contemplated to block near-infraredlight (750˜1200 nm) with a near-infrared absorption filter in thedisplay and the concept has already been implemented. Usually, for thispurpose, a resin film containing a color having a high absorption in thewavelength region of 750˜1200 nm with only a little absorption ofvisible light has been employed and, therefore, a color with gooddurability, high absorption coefficient and good compatibility with theresin used is being wanted.

[0014] As to said polymethine compound, a large number of specificcompounds are already known and there also are known compounds having acyclic structure introduced as part of the methine chain for increaseddurability. For example, as compounds having substituent groups whichare partly similar to those of the compound of the invention (CompoundA), a heptamethine compound having bis-indolyl groups on both sides isdisclosed in Example 60 on page 65 of JP Kokai H1-153753.

[0015] This compound, however, is distinct from the compound describedin instant application in that the former has a shorter methine chainand has an absorption maximum at 796 nm. Therefore, it absorbs littlelight of a high-output YAG laser having a stable emission band at 1064nm which is currently under investigation. Thus, the compound is too lowin sensitivity and cannot be used as a near-infrared absorbing materialexploiting said laser as a light source.

OBJECT AND SUMMARY OF THE INVENTION

[0016] The object of the present invention is to provide a polymethinecompound suitable as a near-infrared absorbing material which absorbslittle in the visible region of the spectrum, has a large absorptioncapacity in the oscillation band of a YAG laser which is a stable sourceof high-output laser light, as well as high solvent solubility and highlight stability, and as such can be used with advantage in thephotothermal conversion layer of laser thermal recording materials andoriginal plates for direct printing plate making.

[0017] As the result of intensive investigations made for accomplishingthe above object, the inventors of the present invention discovered thata novel polymethine compound absorbs little in the visible region of thespectrum, has good sensitivity to a YAG laser having an oscillation bandof 900˜1100 nm as well as high photothermal conversion efficiency, andcan be used as a near-infrared absorbing material which can be easilyprocessed for various end uses, and have accordingly developed thepresent invention.

[0018] The present invention in its first aspect relates to apolymethine compound of the following general formula (1)

[0019] (wherein R₁ and R₃ each independently represents an unsubstitutedor substituted alkyl group, a cycloalkyl group of 5˜7 carbon atoms or anunsubstituted or substituted aryl group; R₂ and R₄ each independentlyrepresents an unsubstituted or substituted alkyl group or anunsubstituted or substituted aryl group; R₅ and R₆ each independentlyrepresents a hydrogen atom, an unsubstituted or substituted alkyl groupor an unsubstituted or substituted alkoxy group; L represents anunsubstituted or substituted alkylene group of 2˜4 carbon atoms which isnecessary for formation of a cyclic structure; X represents a hydrogenatom, a halogen atom or a substituted amino group; Z represents acharge-neutralizing ion)

[0020] The present invention in its second aspect relates to a processfor producing a polymethine compound of claim 1 which comprisescondensing an indolylethylene compound of the following general formula(2) with a diformyl compound of the following general formula (3) or adianil compound of the following general formula (4) in the presence ofan alkali metal salt by means of a dehydrative organic acid.

[0021] (wherein R₁ and R₃ each independently represents an unsubstitutedor substituted alkyl group, a cycloalkyl group of 5˜7 carbon atoms, oran unsubstituted or substituted aryl group; R₂ and R₄ each independentlyrepresents an unsubstituted or substituted alkyl group or anunsubstituted or substituted aryl group; R₅ and R₆ each independentlyrepresents a hydrogen atom, an unsubstituted or substituted alkyl group,or an unsubstituted or substituted alkoxy group)

[0022] (wherein X represents a hydrogen atom, a halogen atom or asubstituted amino group; L represents an unsubstituted or substitutedalkylene group of 2˜4 carbon atoms which is necessary to form a cyclicstructure)

[0023] (wherein X and L have the same meanings as above)

[0024] The present invention in its third aspect relates to anear-infrared absorbing material comprising the polymethine compoundaccording to said first aspect of the invention.

[0025] The present invention in its fourth aspect relates to an originalplate for direct printing plate making comprising a support and aphotothermal conversion layer disposed thereon, said photothermalconversion layer containing the polymethine compound according to saidfirst aspect of the invention.

[0026] The present invention in its fifth aspect relates to a method offabricating a printing plate which comprises irradiating the originalplate for direct printing plate making according to said fourth aspectof the invention using a YAG laser having an emission band of 900˜1100nm as a light source.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1 is an IR absorption spectrum of the polymethine compoundaccording to Example 1;

[0028]FIG. 2 is an IR absorption spectrum of the polymethine compoundaccording to Example 2;

[0029]FIG. 3 is an IR absorption spectrum of the polymethine compoundaccording to Example 3;

[0030]FIG. 4 is an IR absorption spectrum of the polymethine compoundaccording to Example 4;

[0031]FIG. 5 is an IR absorption spectrum of the polymethine compoundaccording to Example 5;

[0032]FIG. 6 is an IR absorption spectrum of the polymethine compoundaccording to Example 6;

[0033]FIG. 7 is an IR absorption spectrum of the polymethine compoundaccording to Example 7;

[0034]FIG. 8 is a VIS-NIR absorption spectrum of the polymethinecompound according to Example 1 in diacetone alcohol;

[0035]FIG. 9 is a VIS-NIR absorption spectrum of the polymethinecompound according to Example 2 in diacetone alcohol; and

[0036]FIG. 10 is a VIS-NIR absorption spectrum of the polymethinecompound according to Example 3 in diacetone alcohol.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0037] The present invention is now described in detail.

[0038] [Polymethine compound]

[0039] To begin with, the polymethine compound of the following generalformula (1), which constitutes the first aspect of the invention, isdescribed below.

[0040] (wherein R₁ and R₃ each independently represents an unsubstitutedor substituted alkyl group, a cycloalkyl group of 5˜7 carbon atoms or anunsubstituted or substituted aryl group; R₂ and R₄ each independentlyrepresents an unsubstituted or substituted alkyl group or anunsubstituted or substituted aryl group; R₅ and R₆ each independentlyrepresents a hydrogen atom, an unsubstituted or substituted alkyl groupor an unsubstituted or substituted alkoxy group; L represents anunsubstituted or substituted alkylene group of 2˜4 carbon atoms which isnecessary for formation of a cyclic structure; X represents a hydrogenatom, a halogen atom or a substituted amino group; Z represents acharge-neutralizing ion)

[0041] The unsubstituted alkyl groups for R₁ and R₃ are preferablystraight-chain or branched-chain alkyl groups containing 1˜18 carbonatoms, more preferably straight-chain or branched-chain alkyl groups of1˜8 carbon atoms. As specific examples, there can be mentioned methyl,ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, n-pentyl,isopentyl, neopentyl, n-hexyl, isohexyl, sec-hexyl, 2-ethylbutyl,n-heptyl, isoheptyl, sec-heptyl, n-octyl, 2-ethylhexyl, n-decyl,n-dodecyl, n-pentadecyl and n-octadecyl.

[0042] The substituted alkyl groups for R₁ and R₃ are preferablyalkoxyalkyl, sulfoalkyl and carboxyalkyl, and, among various alkoxyalkylgroups, those containing a total number of carbon atoms from 2 to 8 areparticularly preferred. As specific examples, there can be mentioned2-methoxyethyl, 3-methoxypropyl, 4-methoxybutyl, 2-ethoxyethyl,3-ethoxypropyl, 4-ethoxybutyl, 2-n-propoxyethyl, 2-iso-propoxyethyl,3-n-propoxypropyl, 4-n-propoxybutyl, 2-(2-methoxyethyl)ethyl and2-(2-ethoxyethoxy)ethyl.

[0043] The preferred sulfoalkyl for R₁ and R₃ includes straight-chain orbranched-chain sulfoalkyl groups containing 1˜18 carbon atoms, withstraight-chain or branched-chain sulfoalkyl groups containing 1˜8 carbonatoms being particularly preferred. It is also preferable that at leastone of the sulfoalkyl groups for R₁ and R₃ be in the form of a salt withan alkali metal ion or an alkylammonium ion. As specific examples, therecan be mentioned 2-sulfoethyl, 3-sulfopropyl, 3-sulfobutyl,4-sulfobutyl, 4-sulfo-3-methylbutyl, 2-(3-sulfopropoxy)ethyl,2-hydroxy-3-sulfopropyl, 3-sulfo-2-(2-ethoxy)ethoxypropoxy,5-sulfopentyl, 6-sulfohexyl, 8-sulfooctyl and 6-sulfo-2-ethylhexyl, andany of these groups may be in the form of a salt with an alkali metalion or an alkylammonium ion.

[0044] The preferred carboxyalkyl for R₁ and R₃ includes straight-chainor branched-chain carboxyalkyl groups each containing a total of 2˜18carbon atoms, with straight-chain or branched-chain carboxyalkyl groupseach containing a total of 2˜9 carbon atoms being particularlypreferred. It is also preferable that at least one of such carboxyalkylgroups for R₁ and R₃ be in the form of a salt with an alkali metal ionor an alkylammonium ion. As specific examples, there can be mentioned2-carboxyethyl, 3-carboxypropyl, 3-carboxybutyl, 4-carboxybutyl,4-carboxy-3-methylbutyl, 2-(3-carboxypropoxy)ethyl,2-hydroxy-3-carboxypropyl, 3-carboxy-2-(2-ethoxy)ethoxypropoxy,5-carboxypentyl, 6-carboxyhexyl, 8-carboxyoctyl and6-carboxy-2-ethylhexyl, each of which may be in the form of a salt withan alkali metal ion or an alkylammonium ion.

[0045] The preferred cycloalkyl of 5˜7 carbon atoms for R₁ and R₃include cyclohexyl and cyclopentyl, with cyclohexyl being particularlypreferred.

[0046] The preferred unsubstituted aryl groups for R₁ and R₃ are phenyland naphthyl, with phenyl being particularly preferred.

[0047] The preferred substituted aryl groups for R₁ and R₃ are phenylgroups substituted by a straight-chain alkyl group of 1˜4 carbon atomsor an alkoxy group of 1˜4 carbon atoms, with phenyl substituted bymethyl, ethyl, methoxy or ethoxy being particularly preferred. Asspecific examples, 4-methylphenyl, 4-methoxyphenyl, 4-ethylphenyl and4-ethoxyphenyl can be mentioned.

[0048] R₁ and R₃ each is preferably an alkyl group of 1˜18 carbon atoms,an alkoxyalkyl group containing a total of 2˜8 carbon atoms, asulfoalkyl group containing 1˜18 carbon atoms, a carboxyalkyl groupcontaining a total of 2˜18 carbon atoms, a cyclohexyl group, a phenylgroup, or a phenyl group substituted by an alkyl group of 1˜4 carbonatoms or an alkoxy group containing 1˜4 carbon atoms.

[0049] The unsubstituted alkyl group referred to above for R₂ and R₄ ispreferably a straight-chain or branched-chain alkyl group of 1˜8 carbonatoms, more preferably a straight-chain or branched-chain alkyl group of1˜4 carbon atoms. As specific examples, methyl, ethyl, n-propyl,isopropyl, n-butyl, isobutyl, sec-butyl and n-octyl can be mentioned.

[0050] The substituted alkyl group referred to above for R₂ and R₄ ispreferably an alkoxyalkyl group, more preferably an alkoxyalkyl groupcontaining a total of 2˜8 carbon atoms. As specific examples, there canbe mentioned 2-methoxyethyl, 3-methoxypropyl, 4-methoxybutyl,2-ethoxyethyl, 3-ethoxypropyl, 4-ethoxybutyl, 2-n-propoxyethyl,2-iso-propoxyethyl, 3-n-propoxypropyl, 4-n-propoxybutyl,2-(2-methoxyethoxy)ethyl and 2-(2-ethoxyethoxy)ethyl.

[0051] The unsubstituted aryl group referred to above for R₂ and R₄includes phenyl and naphthyl, although phenyl is preferred.

[0052] The substituted aryl group referred to above for R₂ and R₄ ispreferably a phenyl group substituted by a straight-chain alkyl group of1˜4 carbon atoms or an alkoxy group containing 1˜4 carbon atoms, morepreferably a phenyl group substituted by methyl, ethyl, methoxy orethoxy. As specific examples, 4-methylphenyl, 4-methoxyphenyl,4-ethylphenyl and 4-ethoxyphenyl can be mentioned.

[0053] The preferred groups for R₂ and R₄ include alkyl groups of 1˜8carbon atoms, alkoxyalkyl groups each containing a total of 2˜8 carbonatoms, a phenyl group, or a phenyl group substituted by an alkyl groupof 1˜4 carbon atoms or an alkoxy group containing 1˜4 carbon atoms.

[0054] The unsubstituted alkyl group referred to above for R₅ and R₆ ispreferably a straight-chain or branched chain alkyl group of 1˜8 carbonatoms, more preferably a straight-chain or branched-chain alkyl group of1˜4 carbon atoms. As specific examples, there can be mentionedmethyl,ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, n-pentyl,isopentyl, neopentyl, n-hexyl, isohexyl, sec-hexyl, 2-ethylbutyl,n-heptyl, isoheptyl, sec-heptyl, n-octyl and 2-ethylhexyl.

[0055] Referring to the substituted alkyl group referred to above for R₅and R₆, the substituent includes alkyloxy, alkylthio, hydroxy andhalogen, among others, although alkyloxy is preferred. The alkylsubstituted by alkyloxy, that is to say alkoxyalkyl, for R₅ and R₆ ispreferably one containing a total of 2˜8 carbon atoms. As examples,there can be mentioned 2-methoxyethyl, 3-methoxypropyl, 4-methoxybutyl,2-ethoxyethyl, 3-ethoxypropyl, 4-ethoxybutyl, 2-n-propoxyethyl,2-iso-propoxyethyl, 3-n-propoxypropyl, 4-n-propoxybutyl,2-(2-methoxyethoxy)ethyl and2-(2-ethoxyethoxy)ethyl.

[0056] The unsubstituted alkoxy group referred to above for R₅ and R₆ ispreferably a straight-chain or branched-chain alkoxy group containing1˜8 carbon atoms, more preferably a straight-chain or branched-chainalkoxy group containing 1˜4 carbon atoms. As specific examples, therecan be mentioned methoxy, ethoxy, n-propoxy, n-butoxy, iso-butoxy,sec-butoxy, n-pentoxy, n-octyloxy, 2-ethylhexyloxy, 2-methoxyethoxy and2-ethoxyethoxy.

[0057] With regard to the substituted alkoxy group referred to above forR₅ and R₆, the substituent includes alkyloxy, alkylthio, hydroxy andhalogen, although alkyloxy is particularly preferred. The alkoxy groupsubstituted by an alkyloxy group, that is to say alkoxyalkoxy, for R₅and R₆ is preferably one having a total of 2˜8 carbon atoms. As specificexamples, there can be mentioned 2-methoxyethoxy, 3-methoxypropoxy,4-methoxybutoxy, 2-ethoxyethoxy, 3-ethoxypropoxy, 4-ethoxybutoxy,2-n-propoxyethoxy, 2-iso-propoxyethoxy, 3-n-propoxypropoxy,4-n-propoxybutoxy, 2-(2-methoxyethoxy)ethoxy and2-(2-ethoxyethoxy)ethoxy.

[0058] R₅ and R₆ each is preferably a hydrogen atom, an alkyl group of1˜8 carbon atoms, an alkoxy group containing 1˜8 carbon atoms, analkoxyalkyl group containing a total of 2˜8 carbon atoms or analkoxyalkoxy group containing a total of 2˜8 carbon atoms.

[0059] L represents an alkylene group of 2˜4 carbon atoms, which iseither substituted or unsubstituted and forms a ring in combination withthe carbon atom attached directly to X and the carbon atom on eitherside thereof, or a total of 3 carbon atoms.

[0060] The unsubstituted alkylene group for L is an alkylene group of2˜4 carbon atoms, preferably an alkylene group of 2˜3 carbon atoms. Asspecific examples, ethylene, propylene and butylene can be mentioned.

[0061] The substituted alkylene group for L is an alkylene groupcontaining 2˜4 carbon atoms and having a substituent or substituentsselected from among straight-chain or branched-chain alkyl groups of 1˜4carbon atoms. Particularly preferred is an alkylene group of 2˜3 carbonatoms having methyl or ethyl as a substituent or substituents. Asspecific examples, there can be mentioned 2-methylpropylene,2-ethylpropylene and 2,2-dimethylpropylene.

[0062] X is preferably a hydrogen atom, a halogen atom, e.g. F, Cl, Bror I, an ethylamino group, a phenylamino group, or a diphenylaminogroup, more preferably Cl, Br, or diphenylamino.

[0063] Z represents a charge-neutralizing ion, including F⁻, Cl⁻, Br⁻,I⁻, Bro₄ ⁻, C1o₄ ⁻, p-toluenesulfonate, CH₃SO₃ ⁻, BF₄ ⁻, CH₃CO₂ ⁻,CF₃CO₂ ⁻, PF₆ ⁻, SbF₆ ⁻, Na⁺, K⁺, and triethylammonium ion, amongothers. Particularly preferred is Cl⁻, Br⁻, I⁻, C1O₄ ⁻, BF₄ ⁻, CF₃CO₂ ⁻,PF₆ ⁻, SbF₆ ⁻, CH₃SO₃ ⁻, p-toluenesulfonate, Na⁺, K⁺or triethylammoniumion.

[0064] The following is a partial and by no means exhaustive listing ofpreferred species of the polymethine compound of general formula (I)according to the present invention.

[0065] Among the above specific compounds (1)˜(51), the compoundsrepresented by the following general formula (5) can also be representedby the following general formula (6).

[0066] (wherein R₁˜R₆, X and L have the same meanings as definedhereinbefore; M represents Na, K or triethylammonium)

[0067] By way of illustration, the specific compound (46) can be writtenas:

[0068] [process for producing the polymethine compound]

[0069] The polymethine compound of the present invention can be producedby, for example, subjecting a bisindolylethylene compound of generalformula (2) and either a diformyl compound of general formula (3) or adianil compound of the following general formula (4) to condensationreaction in the presence of an alkali metal salt in a dehydrativeorganic acid. Incidentally, Z in general formula (1) is derived from theacid residue of the alkali metal salt used. It should also be noted thatZ can be changed to a different charge-neutralizing ion by an ionexchange technique, for example by dissolving the product of the abovecondensation reaction in a solvent, adding not less than one equivalentof an alkaline reagent to neutralize the acid residue and adding adifferent acidic reagent to the neutralized solution.

[0070] (wherein R₁˜R₅ have the same meanings as defined hereinbefore)

[0071] (wherein X and L have the same meanings as defined hereinbefore)

[0072] (wherein X and L have the same meanings as defined hereinbefore)

[0073] Referring to the above condensation reaction, the alkali metalsalt includes KClO₄, KBF₄, sodium p-toluenesulfonate, sodiummethanesulfonate, potassium acetate, sodium propionate, NaI and KBr,among others.

[0074] The alkali metal salt is used in a proportion of generally about0.1˜5 moles, preferably about 1˜2.5 moles, per mole of the compoundrepresented by the general formula (2).

[0075] The dehydrative organic acid includes but is not limited toacetic anhydride, propionic anhydride, butyric anhydride andγ-butyrolactone.

[0076] Such a dehydrative organic acid is used in a proportion ofgenerally about 10˜100 moles, preferably about 20˜50 moles, per mole ofthe compound represented by the general formula (2).

[0077] As to the relative amount of the compound of general formula (2)and the compound of general formula (3) or (4), generally about 0.2˜1.5moles, preferably about 0.4˜0.7 mole, of the latter is used per mole ofthe former.

[0078] The above reaction proceeds well at a temperature of generallyabout 10˜150° C., preferably 40˜120° C., and goes to completiongenerally in several minutes to about 3 hours.

[0079] After completion of the reaction, the objective product can beeasily separated from the reaction mixture by injecting water or asolvent, e.g. methanol, ethanol, n-propanol, isopropyl alcohol orn-butanol, into the cooled reaction mixture or pouring the cooledreaction mixture in water or a solvent, e.g. methanol, ethanol,n-propanol, isopropyl alcohol or n-butanol. The reaction product thusobtained can be further purified by the conventional purificationtechniques such as recrystallization, column chromatography and soforth.

[0080] The compound of general formula (2) can be easily synthesized byreacting the corresponding indole compound with acetyl chloride inacetic anhydride at 50˜60° C. for several hours.

[0081] The diformyl type compound of general formula (3) can besynthesized by, for example, the process described in Journal of OrganicChemistry, 42, 885-888 (1977). The dianil compound of general formula(4) can be easily synthesized by reacting the diformyl type compound ofgeneral formula (3) with aniline hydrochloride.

[0082] [Near-infrared absorbing material]

[0083] The near-infrared absorbing material of the present invention maycontain a binder resin and/or other component in addition to thepolymethine compound of formula (1).

[0084] Furthermore, in addition to the polymethine compound of generalformula (1), various known near-infrared absorbing materials can beconcomitantly used within the range not departing from the spirit of theinvention.

[0085] The near-infrared absorbing materials which can be usedconcomitantly include the common pigments, such as carbon black andaniline black, but also the various pigment type and dye type colorsdescribed in Near-Infrared-Absorbing Colors (p. 45-51) in “Kagaku Kogyo(Chemical Industry)” May, 1986 issue) and “Development and Market Trendof Functional Colors in the Ninties” CMC (1990), Chapter 2-2.3., such aspolymethine colors (cyanine colors), phthalocyanine colors, dithiolmetal complex salt colors, naphthoquinone and anthraquinone colors,triphenylmethane (analogous) colors, aminium and diimmonium colors,etc., as well as azo colors, indoaniline metal complex colors,intermolecular CT colors and so forth.

[0086] The binder resin is not particularly restricted but includeshomopolymers and copolymers of acrylic monomers such as acrylic acid,mthacrylic acid, acrylic esters, methacrylic esters, etc.; cellulosicpolymers such as methylcellulose, ethylcellulose, cellulose acetate,etc.; vinyl polymers and vinyl compound copolymers such as polystyrene,vinyl chloride-vinyl acetate copolymer, polyvinylpyrrolidone, polyvinylbutyral, polyvinyl alcohol, etc.; condensation polymers such aspolyesters and polyamides, rubber type thermoplastic polymers such asbutadiene-styrene copolymer, and polymers produced by the polymerizationand crosslinking of photopolymerizable compounds such as epoxycompounds, among others.

[0087] In the application of the near-infrared absorbing material of theinvention to optical recording materials such as optical cards, suchmaterials can be fabricated by coating a glass, plastic resin or othersubstrate with a solution of the near-infrared absorbing material in anorganic solvent by any of the various techniques heretofore tried ingeneral with success, such as spin coating. The resin which can be usedas the material of said substrate is not particularly restricted butincludes acrylic resin, polyethylene resin, vinyl chloride resin,vinylidene chloride resin and polycarbonate resin, among others. Thesolvent to be used for spin coating is not particularly restricted butincludes hydrocarbons, halogenated hydrocarbons, ethers, ketones,alcohols and Cellosolves, although alcohol solvents such as methanol,ethanol, propanol, etc. and Cellosolves such as methyl-Cellosolve,ethyl-Cellosolve, etc. are preferred.

[0088] For application of the near-infrared absorbing material of theinvention in the field of near-infrared absorption filters, thermal-rayscreens, or agricultural film, these can be manufactured by mixing thenear-infrared absorbing material of the invention with a plastic resinand, depending on cases, an organic solvent as well and molding themixture into a sheet or film by a conventional technique such asinjection molding or casting. The resin which can be used is notparticularly restricted but includes acrylic resin, polyethylene resin,vinyl chloride resin, vinylidene chloride resin and polycarbonate resin,among others The solvent for use is not particularly restricted butincludes hydrocarbons, halogenated hydrocarbons, ethers, ketones,alcohols and Cellosolves, although alcohol solvents such as methanol,ethanol, propanol, etc. and Cellosolve solvents such asmethyl-Cellosolve and ethyl-Cellosolve are preferred.

[0089] For application of the near-infrared absorption filter to PDP,the usual procedure comprises forming a near-infrared absorption filterlayer on a transparent substrate. The material of said transparentsubstrate is not particularly restricted but may be any material that issubstantially transparent with little absorption and scattering. Forexample, glass, polyolefin resins, amorphous polyolefin resins,polyester resins, polycarbonate resins, poly(meth)acrylate resin,polyvinyl acetate, polyvinyl chloride, polystyrene, polyacrylate resins,polyethersulfone resins, etc. can be mentioned. Particularly preferredare amorphous polyolefin resins, polycarbonate resins,poly(meth)acrylate resins, polyarylate resins and polyethersulfoneresins. These resins may have been formulated with any of theconventional additives in common use in the field. As such additives,there can be mentioned various antioxidants, flame retardants, thermalaging inhibitors, ultraviolet absorbers, lubricants and antistaticagents, among others.

[0090] In using the near-infrared absorbing material of the invention ina recording material such as a laser thermographic copying material or alaser thermal recording material, the near-infrared absorbing materialmay be used as formulated with a color-forming component or a colorcomponent or a discrete layer containing a color-forming component or acolor component may be provided. As the color-forming component or colorcomponent, sublimable dyes or pigments, electron-donating dyeprecursor-electron-accepting compound systems, and the systemsheretofore explored in which images are formed by heat-inducedphysicochemical changes in polymerizable polymers or the like can beemployed. For example, the color component of a laser thermographiccopying material is not particularly restricted but, as pigment typecomponents, there can be mentioned inorganic pigments such as titaniumdioxide, carbon black, zinc oxide, Prussian blue, cadmium sulfide, ironoxide, chromates of lead, zinc, barium and calcium, etc. and organicpigments such as azo, thioindigo, anthraquinone, anthanthrone,triphenodioxazine, phthalocyanine, quinacridone and other pigments. Thedye which can be used includes acid dyes, direct dyes, disperse dyes,oil-soluble dyes and metal-containing oil-soluble dyes, among others.

[0091] The color-forming component for a laser thermal recordingmaterial is not particularly restricted but the substances which haveheretofore been utilized in thermal recording materials can be employed.As electron-donating dye precursor, there is employed a compound havinga partial skeleton in the form of a lactone, lactam, sultone,spiropyran, ester, amide, or the like, and developing color by givingoff an electron or receiving a proton, for example from an acid, withsaid partial skeleton being opened or cleaved on contact with anelectron-accepting compound. For example, there can be mentionedtriphenylmethane compounds, fluorene compounds, phenothiazine compounds,indolyl-phthalide compounds, leucoauramine compounds, rhodamine-lactamcompounds, triphenylmethane compounds, triazene compounds, spiropyrancompounds, fluorene compounds and so forth. As the electron-acceptingcompound, there can be mentioned phenolic compounds, organic acids ormetal salts thereof, and hydroxybenzoic esters, among others. [originalplate for direct printing plate making]

[0092] The polymethine compound of the present invention can be usedwith advantage as a near-infrared absorbing material for an originalplate for direct printing plate making. The original plate for directprinting plate making comprises a support and a photothermal conversionlayer disposed thereon. Optionally, a silicone rubber layer may besuperimposed on said photothermal conversion layer. Furthermore, aprotective layer or the like may also be formed in superimposition.

[0093] Such a photothermal conversion layer comprises an image-formingcomponent and a binder resin in addition to the above-describedpolymethine compound of the invention. Alternatively, a layer containingthe image-forming component may be built up on a photothermal conversionlayer.

[0094] As the image-forming component, the conventionally exploitedmaterials which form images by undergoing physicochemical changes whenheated can be utilized without any particular restriction. For example,a system comprising a microencapsulated heat-meltable substance and abinder resin as disclosed in JP Kokai H3-108588; a system comprising ablocked isocyanate and so on in combination with an activehydrogen-containing binder as disposed on a support having a hydrophilicsurface as disclosed in JP Kokoku S62-164049; a system comprising amicroencapsulated oleophilic component, a hydrophilic binder polymer,etc. as disclosed in JP Kokai H7-1849; a composition comprising an acidprecursor, a vinyl ether group-containing compound, an alkali-solubleresin, etc. as disclosed in JP Kokai H8-220752; a composition comprisinga hydroxy-containing macromolecular compound, o-naphthoquinone diazidecompound, etc. as disclosed in JP Kokai H9-5993; a compositioncomprising nitrocellulose, etc. as disclosed in JP Kokai H9-131977; anda composition comprising a polymerization initiator and an ethylenicallyunsaturated monomer, oligomer or macromonomer as disclosed in JP KokaiH9-146264, among others, can be mentioned. Depending on cases, the imagearea can be formed by laminating a silicone rubber layer on aphotothermal conversion layer (a light-sensitive layer or a thermalrecording layer) and, after exposure to light, bringing into intimatecontact or removing the silicone rubber layer as disclosed in JP KokaiH9-80745, JP Kokai H9-131977 and JP Kokai H9-146264, among otherpublications.

[0095] The binder resin for use in the photothermal conversion layer isnot particularly restricted but includes homopolymers and copolymers ofacrylic monomers such as acrylic acid, mthacrylic acid, acrylic esters,methacrylic esters, etc.; cellulosic polymers such as methylcellulose,ethylcellulose, cellulose acetate, etc.; vinyl polymers and vinylcompound copolymers such as polystyrene, vinyl chloride-vinyl acetatecopolymer, polyvinylpyrrolidone, polyvinyl butyral, polyvinyl alcohol,etc.; condensation polymers such as polyesters and polyamides, rubbertype thermoplastic polymers such as butadiene-styrene copolymer, andpolymers produced by the polymerization and crosslinking ofphotopolymerizable compounds such as epoxy compounds, among others.

[0096] The printing original plate according to the invention shouldhave a degree of flexibility that permits setting on the ordinaryprinting press and, at the same time, is sturdy enough to withstand theload applied in printing. Thus, the support which can be used includes asheet of paper, plastic (e.g. polyethylene, polypropylene, polystyreneor the like)-laminated paper, a metal plate made of e.g. aluminum(inclusive of aluminum alloys) , zinc, copper or the like, or a plasticfilm made of, for example, cellulose diacetate, cellulose triacetate,cellulose butyrate, polyethylene terephthalate, polyethylene,polystyrene, polypropylene, polycarbonate, polyvinyl acetal or otherplastic material. As typical support materials, coated paper, aluminumor other metal sheet, polyethylene terephthalate or other plastic film,rubber, and various composites thereof can be mentioned. The preferredmaterials are aluminum, aluminum alloys and plastic film. The thicknessof the support is 25 μm˜3 mm, preferably 100 μm˜500 μm.

[0097] Usually, the original plate for printing is fabricated bydispersing or dissolving the polymethine compound, image-formingcomponent, binder resin, etc. in an organic solvent or the like andcoating a support with the resulting dispersion or solution.

[0098] The solvent which can be used as above includes water; alcoholssuch as methanol, isopropyl alcohol, isobutyl alcohol, cyclopentanol,cyclohexanol, diacetone alcohol, etc.; Cellosolve solvents such asmethyl-Cellosolve, ethyl-Cellosolve, etc.; aromatic hydrocarbon solventssuch as toluene, xylene, chlorobenzene, etc.; esters such as ethylacetate, butyl acetate, isoamyl acetate, methyl propionate, etc.;ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone,cyclohexanone, etc.; chlorinated hydrocarbons such as methylenechloride, chloroform, trichloroethylene, etc.; ethers such astetrahydrofuran, dioxane, etc.; and aprotic polar solvents such asN,N-dimethylformamide and N-methylpyrrolidone.

[0099] Between the support and the photothermal conversion layer may beinterposed a primer layer for improved adhesion and improved printingcharacteristics. The support itself may be subjected to surfacetreatment. The primer layer which can be disposed includes curedartifacts obtained by photocuring of various photosensitive polymersbefore formation of the photothermal conversion layer as disclosed in JPKokai S60-22903, the cured artifact obtained by the heat-curing of anepoxy resin as disclosed in JP Kokai S62-50760; a hardened gelatin layeras disclosed in JP Kokai H3-200965; the artifact constructed by using aurethane resin and a silane coupling agent as disclosed in JP KokaiH3-200965; and the artifact constructed by using a urethane resin asdisclosed in JP Kokai H3-273248.

[0100] To provide a protective film for protecting the surface of thephotothermal conversion layer or of the silicone rubber layer, atransparent film, such as a film of polyethylene, polypropylene,polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol,polyethylene terephthalate, cellophane or the like, may be laminated orsuch a film may be applied after stretching.

[0101] The original plate for direct printing plate making according tothe invention is compatible with a YAG laser having a defined emissionband. Thus, for the fabrication of a duplicate printing plate from thisoriginal plate, the original plate is irradiated with laser light by theknown technique using a YAG laser having an emission band of 900˜1100 nmas the light source to form image areas or non-image areas, wherebydigital data from a computer or the like are recorded.

EXAMPLES

[0102] The following examples are intended to describe the presentinvention in further detail and should by no means be construed asdefining the scope of the invention.

Example 1

[0103] Polymethine compound [synthesis of specific compound (1)]

[0104] To 14 ml of acetic anhydride were added 2.00 g of theindolylethylene compound of general formula (2) (R₁=R₃=ethyl;R₂=R₄=phenyl; R₅=R₆=hydrogen atom), 0.81 g of the dianil compound ofgeneral formula (4) (L=propylene; X =Cl) and 1.28 g of potassiumperchlorate, and the mixture was stirred at 95˜100° C. for 30 minutes.After cooling, the reaction mixture was poured into 150 ml of water. Theresulting precipitate was recovered by filtration, rinsed with water,dried and recrystallized from methanol to give 1.93 g of specificcompound (1).

[0105] The elemental analysis, melting point, maximum absorptionwavelength (λmax) and gram-absorption coefficient (εg) of this compoundwere as follows.

[0106] Elemental analysis (C₇₆H₆₆Cl₂N₄O₄): MW=1170.3 C H N Calcd. (%)78.00 5.68 4.79 Found (%) 78.02 5.71 4.77

[0107] Melting point (° C.): 179˜181° C. λmax:1007 nm (in diacetonealcohol) Εg: 1.18×10⁵ ml/g•cm

[0108] The IR spectrum of the compound obtained is shown in FIG. 1.

[0109] The VIS-NIR absorption spectrum of the same compound is shown inFIG. 8.

Example 2

[0110] Polymethine compound [synthesis of specific compound (2)]

[0111] To 14 ml of acetic anhydride were added 2.0 g of theindolylethylene compound of general formula (2) (R₁=R₃=ethyl;R₂=R₄=phenyl; R₅=R₆=hydrogen atom), 0.72 g of the dianil compound ofgeneral formula (4) (L=propylene; X=Cl) and 1.16 g of potassiumborofluoride, and the mixture was stirred at 95˜100° C. for 60 minutes.After cooling, the reaction mixture was poured into 150 ml of water. Theresulting precipitate was recovered by filtration, rinsed with water,dried and recrystallized from methanol to give 2.01 g of specificcompound (2).

[0112] The elemental analysis, melting point, maximum absorptionwavelength (λmax) and gram-absorption coefficient (εg) of this compoundwere as follows.

[0113] Elemental analysis (C₇₆H₆₆BClF₄N₄): MW=1157.6 C H N Calcd. (%)78.85 5.75 4.84 Found (%) 78.89 5.77 4.81

[0114] Melting point (° C.): 195˜197° C. λmax: 1007 nm (in diacetonealcohol) εg: 1.21×10⁵ ml/g•cm

[0115] The IR spectrum of the compound obtained is shown in FIG. 2.

[0116] The VIS-NIR absorption spectrum of the same compound is shown inFIG. 9.

Example 3

[0117] Polymethine compound [synthesis of specific compound (17)]

[0118] To 14 ml of acetic anhydride were added 1.47 g of theindolylethylene compound of general formula (2) (R¹=R₃=ethyl;R₂=R₄=phenyl; R₅=R₆=hydrogen atom), 0.81 g of the dianil compound ofgeneral formula (4) (L=propylene; X=Cl) and 1.28 g of potassiumperchlorate, and the mixture was stirred at 115˜120° C. for 2.5 hours.After cooling, the reaction mixture was poured into 150 ml of water. Theresulting precipitate was recovered by filtration, rinsed with water,dried and recrystallized from methanol to give 1.64 g of specificcompound (17).

[0119] The elemental analysis, melting point, maximum absorptionwavelength (λmax) and gram-absorption coefficient (εg) of this compoundwere as follows.

[0120] Elemental analysis (C₅₆H₅₈Cl₂N₄O₄): MW=922.0 C H N Calcd. (%)72.95 6.34 6.08 Found (%) 73.03 6.27 6.03

[0121] Melting point (° C.): 161˜163° C. λmax: 976 nm (in diacetonealcohol) εg: 1.29×10⁵ ml/g•cm

[0122] The IR spectrum of the compound obtained is shown in FIG. 3.

[0123] The VIS-NIR absorption spectrum of the same compound is shown inFIG. 10.

Example 4

[0124] Polymethine compound [synthesis of specific compound (18)]

[0125] To 14 ml of acetic anhydride were added 1.47 g of theindolylethylene compound of general formula (2) (R₁=R₃=ethyl;R₂=R₄=methyl; R₅=R₆=hydrogen atom), 0.81 g of the dianil compound ofgeneral formula (4) (L=propylene; X=Cl) and 1.16 g of potassiumborofluoride, and the mixture was stirred at 95˜100° C. for 60 minutes.After cooling, the reaction mixture was poured into 150 ml of water. Theresulting precipitate was recovered by filtration, rinsed with water,dried and recrystallized from methanol to give 1.61 g of specificcompound (18).

[0126] The elemental analysis, melting point, maximum absorptionwavelength (λmax) and gram-absorption coefficient (εg) of this compoundwere as follows.

[0127] Elemental analysis (C₅₆H₅₈BClF₄N₄): MW=909.3 C H N Calcd. (%)73.97 6.43 6.16 Found (%) 73.94 6.46 6.21

[0128] Melting point (° C.): 174˜176° C. λmax: 975 nm (in diacetonealcohol) εg: 1.25×10⁵ ml/g•cm

[0129] The IR spectrum of the compound obtained is shown in FIG. 4.

Example 5

[0130] Polymethine compound [synthesis of specific compound (22)]

[0131] To 14 ml of acetic anhydride were added 1.74 g of theindolylethylene compound of general formula (2) (R₁=R₃=ethyl; R₂=methyl;R₄=phenyl; R₅=R₆=hydrogen atom), 0.81 g of the dianil compound ofgeneral formula (4) (L=propylene; X=Cl) and 1.17 g of potassiumborofluoride, and the mixture was stirred at 95˜100° C. for 2 hours.After cooling, the reaction mixture was poured into 150 ml of water. Theresulting precipitate was recovered by filtration, rinsed with water,dried and recrystallized from methanol to give 1.62 g of specificcompound (22).

[0132] The elemental analysis, melting point, maximum absorptionwavelength (λmax) and gram-absorption coefficient (εg) of this compoundwere as follows.

[0133] Elemental analysis (C₆₆H₆₂BClF₄N₄): MW=1033.5 C H N Calcd. (%)76.70 6.05 5.42 Found (%) 76.64 6.02 5.45

[0134] Melting point (° C.): 192˜194° C. λmax: 989 nm (in diacetonealcohol) εg: 1.09×10⁵ ml/g•cm

[0135] The IR spectrum of the compound obtained is shown in FIG. 5.

Example 6

[0136] Polymethine compound [synthesis of specific compound (28)]

[0137] To 14 ml of acetic anhydride were added 1.71 g of theindolylethylene compound of general formula (2) (R₁=R₃=butyl;R₂=R₄=methyl; R₅=R₆=hydrogen atom), 0.81 g of the dianil compound ofgeneral formula (4) (L=propylene; X=Cl) and 1.28 g of potassiumperchlorate, and the mixture was stirred at 95˜100° C. for 2.0 hours.After cooling, the reaction mixture was poured into 150 ml of water. Theresulting precipitate was recovered by filtration, rinsed with water,dried and recrystallized from methanol to give 1.51 g of specificcompound (28).

[0138] The elemental analysis, melting point, maximum absorptionwavelength (λmax) and gram-absorption coefficient (εg) of this compoundwere as follows.

[0139] Elemental analysis (C₆₄H₇₄Cl₂N₄O₄): MW=1034.2 C H N Calcd. (%)74.33 7.21 5.42 Found (%) 74.29 7.25 5.39

[0140] Melting point (° C.): 161˜163° C. λmax: 985 nm (in diacetonealcohol) 68 g: 1.11×10⁵ ml/g•cm

[0141] The IR spectrum of the compound obtained is shown in FIG. 6.

Example 7

[0142] Polymethine compound [synthesis of specific compound (51)]

[0143] To 14 ml of acetic anhydride were added 1.71 g of theindolylethylene compound of general formula (2) (R₁=R₃=ethyl;R₂=R₄=phenyl; R₅=R₆=hydrogen atom), 0.77 g of the dianil compound ofgeneral formula (4) (L=ethylene; X=Cl) and 1.16 g of potassiumborofluoride, and the mixture was stirred at 95˜100° C. for 2.0 hours.After cooling, the reaction mixture was poured into 150 ml of water. Theresulting precipitate was recovered by filtration, rinsed with water,dried and recrystallized from methanol to give 1.95 g of specificcompound (51).

[0144] The elemental analysis, melting point, maximum absorptionwavelength (λmax) and gram-absorption coefficient (εg) of this compoundwere as follows.

[0145] Elemental analysis (C₇₅H₆₄BClF₄N₄): MW=1143.6 C H N Calcd. (%)78.77 5.64 4.90 Found (%) 78.71 5.66 4.87

[0146] Melting point (° C.): 187˜192° C. λmax: 1034 nm (in diacetonealcohol) εg: 1.08×10⁵ ml/g•cm

[0147] The IR spectrum of the compound obtained is shown in FIG. 7.

[0148] [Maximum absorption wavelength]

[0149] The maximum absorption wavelength (λmax) value of eachpolymethine compound of the invention in diacetone alcohol is comparedwith that of Compound A which is a known compound, as follows. TABLE 1λmax Specific compound (1) 1007 nm  Specific compound (2) 1007 nm Specific compound (17) 976 nm Specific compound (18) 975 nm Specificcompound (22) 989 nm Specific compound (28) 985 nm Specific compound(51) 1034 nm  Compound A 796 nm

Example 8

[0150] Production of near-infrared absorbing material

[0151] A sample of a near-infrared absorbing material was produced bycoating a polyethylene terephthalate (PET) film having an averagethickness of 5 μm with a solution containing 10 g of the binder Delpet80 N (product of Asahi Kasei Kogyo; acrylic resin) and 0.2 g of specificcompound (1) in 90 g of toluene/methyl ethyl ketone (1/1) in a dry filmthickness of about 5 μm using a wire bar.

[0152] A semiconductor-excited YAG laser with a wavelength of 1064 nmwas disposed so that the laser beam diameter on the surface of the abovesample would be 100 μm. The laser power reaching the surface wasadjusted to 2 W and the sample was irradiated with single pulses at apulse width of 20 μs. Observation of the irradiated sample under thelight microscope revealed formation of through-holes with a diameter ofabout 100 μm.

Examples 9˜18

[0153] Production of near-infrared absorbing material

[0154] Using 0.2 g each of the specific compounds mentioned below inTable 2 in lieu of 0.2 g of specific compound (1), samples ofnear-infrared absorbing material were produced in otherwise the samemanner as in Example 8. These samples were subjected to the same YAGlaser irradiation test as in Example 8. As a result, formation ofthrough-holes with a diameter of about 100 μm could be invariablyconfirmed in Examples 9˜18. TABLE 2 Specific compound used Example 9Specific compound (2) Example 10 Specific compound (17) Example 11Specific compound (18) Example 12 Specific compound (22) Example 13Specific compound (28) Example 14 Specific compound (30) Example 15Specific compound (33) Example 16 Specific compound (36) Example 17Specific compound (42) Example 18 Specific compound (51)

Example 19

[0155] Fabrication of original plate for direct printing plate making

[0156] (Formation of an undercoat layer)

[0157] On a 175 μm-thick polyethylene terephthalate film, a gelatinprimer layer was constructed in a dry thickness of 0.2 μm.

[0158] (Formation of a photothermal conversion layer)

[0159] On the gelatin-undercoated polyethylene terephthalate film, acoating dope according to the following recipe was coated in a dry filmthickness of 2 μm to provide a photothermal conversion layer. SolsperseS27000 (product of ICI) 0.4 Nitrocellulose (n-propanol 4.2 content 30%)Xylylenediamine (1 mole) - glycidyl 2.0 methacrylate (4 moles) adductEthyl Michler's ketone 0.2 Tetrahydrofuran 90  

[0160] (Polyurethane, product of Dainippon Ink Chemical) Amount in partsby weight Specific compound (1) 0.1 Crisvon 3006 LV 5.0

[0161] (Formation of a silicone rubber layer)

[0162] A coating dope according to the following recipe was coated in adry thickness of 2 μm on top of said photothermal conversion layer toprovide a silicone rubber layer. Amount in parts by weight α,ω-Divinylpolydimethylsiloxane 9.0 (degree of polymerization ca 700)(CH₃)₃-Si-O-(SiH(CH₃)-O)₈-Si(CH₃)₃ 0.6 Polydimethylsiloxane 0.5 (degreeof polymerization ca 8000) Olefin-chloroplatinic acid  0.08 InhibitorHC≡C—C(CH₃)₂-O-Si(CH₃)₃  0.07 Isopar G (product of Esso Chemical) 55  

[0163] The original plate obtained as above was written-in with asemiconductor-excited YAG laser (wavelength 1064 nm) at a beam diameterof 100 μm and a recording energy of 0.75 J/cm². As a result, a siliconeimage with a sharp edge could be obtained. Examples 20˜31 Fabrication oforiginal plate for direct printing plate making

[0164] Using 0.1 weight part each of the specific compounds mentionedbelow in Table 3 in lieu of 0.1 weight part of the specific compound (1)used in Example 19, the procedure of Example 19 was otherwise repeatedto fabricate a printing original plate. These original plates werewritten-in with a YAG laser in the same manner as in Example 19. As aresult, a silicone image with a sharp edge could be invariably obtainedin Examples 20˜31. TABLE 3 Specific compound used Example 20 Specificcompound (2) Example 21 Specific compound (5) Example 22 Specificcompound (11) Example 23 Specific compound (17) Example 24 Specificcompound (18) Example 25 Specific compound (22) Example 26 Specificcompound (25) Example 27 Specific compound (28) Example 28 Specificcompound (29) Example 29 Specific compound (34) Example 30 Specificcompound (38) Example 31 Specific compound (51)

Comparative Example 1

[0165] Except that 0.2 g of the polymethine compound (Compound A)described in JP Kokai H1-153753 and having the chemical formula shownbelow was used in lieu of 0.2 g of specific compound (1), a sample ofnear-infrared absorbing material was prepared by wire-bar coating in adry thickness of about 5 μm in the same manner as in Example 8. Asemiconductor-excited YAG laser with a wavelength of 1064 nm wasdisposed so that the beam diameter on the surface of said sample wouldbe 100 μm. The laser power reaching the surface was adjusted to 2 W andthe sample was irradiated with single pulses at a pulse width of 20 μs.Observation of the irradiated sample under the light microscope showedthat no through-holes could be formed at the laser power of 2 W.

INDUSTRIAL APPLICABILITY

[0166] The polymethine compound of general formula (1) absorbs little inthe visible region of the spectrum and shows an exceptionally highsensitivity to a YAG laser having an emission wavelength of 900˜1100 nm,as well as good light stability, high durability, good solubility invarious solvents and high compatibility with various resins so that itis a compound of great use as a near-infrared absorbing material.Moreover, because of its characteristics mentioned above, thispolymethine compound can be easily made into a coating solution to givea uniform photothermal conversion layer so that it is particularlysuitable for the fabrication of original plate for direct printing platemaking compatible with a YAG laser.

What is claimed is:
 1. A polymethine compound of the following generalformula (1):

(wherein R₁ and R₃ each independently represents an unsubstituted orsubstituted alkyl group, a cycloalkyl group of 5˜7 carbon atoms or anunsubstituted or substituted aryl group; R₂ and R₄ each independentlyrepresents an unsubstituted or substituted alkyl group or anunsubstituted or substituted aryl group; R₅ and R₆ each independentlyrepresents a hydrogen atom, an unsubstituted or substituted alkyl groupor an unsubstituted or substituted alkoxy group; L represents anunsubstituted or substituted alkylene group of 2-4 carbon atoms which isnecessary for formation of a cyclic structure; X represents a hydrogenatom, a halogen atom or a substituted amino group; Z represents acharge-neutralizing ion)
 2. A polymethine compound according to claim 1wherein R₁ and R₃ each represents an alkyl group of 1˜18 carbon atoms,an alkoxyalkyl group containing a total of 2˜8 carbon atoms, asulfoalkyl group of 1˜18 carbon atoms, a carboxyalkyl group containing atotal of 2˜8 carbon atoms, a cyclohexyl group, a phenyl group or aphenyl group having an alkyl group of 1˜4 carbon atoms or an alkoxygroup of 1˜4 carbon atoms.
 3. A polymethine compound according to claim1 wherein R₂ and R₄ each represents an alkyl group of 1˜8 carbon atoms,an alkoxyalkyl group containing a total of 2˜8 carbon atoms, a phenylgroup, or a phenyl group having an alkyl group of 1˜4 carbon atoms or analkoxy group of 1˜4 carbon atoms.
 4. A polymethine compound according toclaim 1 wherein R₅ and R₆ each represents a hydrogen atom, an alkylgroup of 1˜8 carbon atoms, an alkoxy group of 1˜8 carbon atoms, analkoxyalkyl group containing a total of 2˜8 carbon atoms, or analkoxyalkoxy group containing a total of 2˜8 carbon atoms.
 5. Apolymethine compound according to claim 1 wherein L represents anunsubstituted alkylene group of 2˜4 carbon atoms.
 6. A polymethinecompound according to claim 1 wherein X represents H, Cl, Br ordiphenylamino.
 7. A polymethine compound according to claim 1 wherein Zrepresents Cl⁻, Br⁻, I⁻, CLO₄ ³¹ , BF₄ ³¹ , CF₃CO₂ ³¹ , PF₆ ³¹ , SbF₆ ³¹, CH₃SO₃ ³¹ , p-toluenesulfonate, Na⁺, K⁺or triethylammonium ion.
 8. Aprocess for producing a polymethine compound of claim 1 which comprisessubjecting an indolylethylene compound of the following general formula(2) and a diformyl compound of the following general formula (3) or adianil compound of the following general formula (4) to condensationreaction in the presence of an alkali metal salt by using a dehydrativeorganic acid.

(wherein R₁ and R₃ each independently represents an unsubstituted orsubstituted alkyl group, a cycloalkyl group of 5˜7 carbon atoms, or anunsubstituted or substituted aryl group; R₂ and R₄ each independentlyrepresents an unsubstituted or substituted alkyl group or anunsubstituted or substituted aryl group; R₅ and R₆ each independentlyrepresents a hydrogen atom , an unsubstituted or substituted alkylgroup, or an unsubstituted or substituted alkoxy group)

(wherein X represents a hydrogen atom, a halogen atom or a substitutedamino group; L represents an unsubstituted or substituted alkylene groupof 2˜4 carbon atoms which is necessary to form a cyclic structure)

(wherein X and L have the same meanings as above)
 9. A near-infraredabsorbing material comprising the polymethine compound defined inclaim
 1. 10. An original plate for direct printing plate makingcomprising a substrate and as disposed thereon a photothermal conversionlayer containing the polymethine compound defined in claim
 1. 11. Aprocess for manufacturing a printing plate which comprises irradiatingthe original plate for direct printing plate making claimed in claim 10using a laser having an emission band of 900˜1100 nm as a light source.